1. Field of the Invention
The present invention relates to a method for manufacturing an absorbent structure in an absorbent article, such as a sanitary napkin, a tampon, a panty protector, an incontinence guard, a diaper, a bed protector, a wound or sore dressing, a saliva absorbent, and like articles. The invention also relates to an article manufactured according to the method.
2. Discussion of Related Art
Many types of absorbent articles of this kind are known to the art. The absorbent bodies of such articles are typically produced by dry-defibering and fluffing cellulose pulp in roll, bale or sheet form for instance, to form a pulp mat, sometimes admixed with so-called superabsorbents in the pulp mat, these superabsorbents being polymers which are capable of absorbing many times their own weight of water or body fluid.
The pulp body is often compressed so as to enhance its fluid wicking ability and also in order to reduce the bulk of the pulp body and therewith obtain an article which is as compact as possible.
The absorbent body may also include other constituents, for instance constituents which will improve its fluid aquisition properties or its fluid-wicking properties, or to increase its coherent strength, i.e. its coherency, and its ability to withstand deformation in use.
One serious drawback with products of this nature is found in the total absorption capacity of the articles and also in the fact that the articles will often leak long before their total absorption capacity has been fully utilized. Among other things, this is because the body fluid discharged by the wearer is unable to penetrate into the absorption material and to spread to hitherto unused areas of the article quickly enough, but instead leaks from the sides of the sanitary napkin, diaper or incontinence guard. The ability of the materials used in the article to disperse the absorbed fluid throughout the entire absorbent body is thus highly important.
Another problem resides in so-called rewetting, i.e, the transference of body fluid that has already been absorbed back into contact with the wearer's skin as a result of external forces, for instance when the wearer sits down. It is generally desired that the surface of the article that lies proximal to the wearer will remain as dry as possible.
Another desideratum with regard to the majority of hygiene products is that the article shall be thin and soft, so that it can be worn as discretely as possible. For some purposes the compressed absorbent body of the absorbent article is softened to achieve the desired softness. One method to soften an absorbent sheet is described in European Patent Application EP 0 360 472, where the compressed absorbent material is worked between partially cutting rollers and thereby gaining softness. This method however leads among other things to decreased strength in the softened material.
It is known from International Patent Application WO 90/05808 to produce a pulp web which is later defibred, so-called dry-formed roll pulp. Flash-dried fibres of paper pulp, which may consist of thermomechanical pulp, chemi-thermomechanical pulp CTMP, or chemical paper pulp, sulphite or sulphate pulp with a dry solids content of about 80%, is delivered by means of an air stream in a controlled flow to a forming head arranged above a forming wire and there formed into a web that has a per unit area weight of 300-1500 g/m2 and a density of 550-1000 kg/m3. Air is sucked away through a suction box placed beneath the wire. The moisture content in the process shall be 5-30%.
The web is pre-pressed to a density of 550-1000 kg/m3 in order to slightly reduce the bulk of the web, prior to the final pressing stage. The pressed web thus has a mechanical strength which enables it to be rolled-up or handled in sheet form for storage and transportation purposes. The web can be readily defibred and is intended to be convened into fluff for use in the manufacture of absorbent bodies or pads for diapers, sanitary napkins and like articles.